The present invention relates to a welder head, particularly to a welder head for an electric welder of an electrode pressure type.
FIG. 6 shows the welder head of a conventional electric welder of an electrode pressure type. A pressure mechanism 2 made of a pneumatic cylinder and so forth is built in the body 1 of the welder head. A guide 3 is provided with a voltage application terminal 3a and is supported by the body 1 of the welder head so that the guide can be moved up and down. An electrode holder 4 is secured to the guide 3. An upper electrode 5 is attached to the bottom of the electrode holder 4. A lower electrode 6 is opposed to the upper electrode 5. An electric insulator 7 electrically insulates the upper electrode 5 and the lower electrode 6 from each other. A spring 8 is provided between the pressure piston rod 2a of the pressure mechanism 2 and the guide 3.
Since the weight load which acts to between the spring 8 downward is exerted by the guide 3, the electrode holder 4 and the upper electrode 5, the constitution and operation of the spring 8 are designed in consideration of the follow-up property of the upper electrode 5 during welding to workpieces to be welded. Some other conventional electric welders of such type are not provided with such a spring.
Next, the operation will be described. When the workpieces are welded to each other by the above-mentioned welder head, the workpieces (not shown) are placed between the upper and the lower electrodes 5 and 6 and the pressure mechanism 2 is operated to press the workpieces on each other. At that time, the pressure is applied to the workpieces through the spring 8, the guide 3, the electrode holder 4 and the upper electrode 5. While the workpieces remain pressed on each other, a voltage is applied between the electrodes 5 and 6 to weld the workpieces to each other.
If the workpieces or the guide 3 undergo a small vibration, the spring 8 absorbs the vibration so that the pressure applied to the workpieces between the electrodes 5 and 6 is kept at a prescribed level while the electrical current is caused to flow through the workpieces.
For the conventional electric welders not provided with such a follow-up spring, the movement of a pressure mechanism 2 is transmitted to an upper electrode 5 through a guide 3 and an electrode holder 4 as it is. When a large current is caused to flow through workpieces to weld them to each other, an electromagnetic force is generated along the passage of the current to reduce the pressure on the workpieces between an upper and a lower electrode.
Since the spring 8 is provided between the pressure mechanism 2 and the guide 3 in the conventional welder head shown in FIG. 6, the weight load which acts on the spring is large and the mass which affects the inertia of a portion including the upper electrode 5 is large so that the follow-up property of the upper electrode to the workpieces is deteriorated. For that reason, when a large current is caused to momentarily and impulsively flow through the workpieces to weld them to each other under pressure, the electrode or the vicinity thereof vibrates to cause the decrease in the thickness of melt of each workpiece or cause the like, and further, the electrode is made separated from the workpieces or the pressure is instantaneously reduced. As a result, the welding of the workpieces is made defective.